[PATCH] user32: Make functions use display dc thread-safe

[Guo Lv]

The problem is not in get_display_dc() but use the value returned(HDC) without lock.

 
------------------ Original ------------------
From:  "Nikolay Sivov"<bunglehead at gmail.com>;
Date:  Fri, Jan 12, 2018 03:56 PM
To:  "吕果"<lvguo at deepin.com>; "wine-devel"<wine-devel at winehq.org>;
Subject:  Re: [PATCH] user32: Make functions use display dc thread-safe
 
On 1/12/2018 8:39 AM, 吕果 wrote:
> Some functions in sysparams.c invoke get_display_dc to get display dc and
>   then use it without lock mechanism. it will cause condition race in multi-thread.
> 
> PS:
>   I dont't kown how to make a test than can stably run into this problem, but
>   call GetSystemMetrics(SM_CXSCREEN) within a tight loop in different thread
>   will get zero finally.
> 

Hi.

If the issue is get_display_dc() alone, you can use single
compare-exchange call to set static variable safely.